The first major step in the cheese making process is the coagulation of milk by enzymatic hydrolysis of K-casein. The hydrolysis of K-casein leads to destabilization of the colloidal system of the milk. This is followed by aggregation of the micelles into clusters. Over time, the clusters grow in size. This growth in size is followed by crosslinking between chains which eventually transform the milk into a gel or coagulum. Once a desired point is reached in the coagulation process, the coagulum is “cut,” e.g., by traversing with knives to slice the coagulum into small pieces.
Selection of the optimum point to cut the coagulum has been a subject of much research. It has been shown that coagulum strength at cutting effects the recovery of milk components during cheese making. More particularly, milk components not entrapped in the K-casein matrix are lost into the whey. Thus, cutting the coagulum when extremely soft decreases cheese yield due to the increased loss of fat and curd fines. Conversely, cutting when the coagulum is too firm retards syneresis and results in high moisture cheese. Further, it has also been suggested that coagulum strength affects the quality of the returning cheese.
Curd firmness and the rate of firming are affected by many factors. For example, high K-casein concentration increases curd firmness. The time and temperature of milk storage prior to cheese manufacture also affects curd firmness. Homogenization and standardization may also influence curd firmness. Other factors affecting firmness are the breed of the cow from which milk is collected, period of lactation of the cow, milk quality, and type of enzyme used in cheese making.
Cheese makers typically schedule cutting of the coagulum 25 to 30 minutes after adding the enzyme, however the coagulum may not have a consistent strength due to many factors. Many systems have been proposed for determining cutting time.
For example, U.S. Pat. No. 5,172,193, incorporated herein by reference, discloses a method (including a mathematical algorithm or equation) for predicting the cutting time of a milk coagulum based upon the light backscatter measurements (at 880 nm). Generally, this light backscatter technology is known to provide accurate results when the milk has consistent coagulating properties. In modern dairy plants several protein sources having different enzyme reactivity are being combined as the substrate for cheese making with the effect being that the coagulating properties vary significantly, and the light backscatter technology needs frequent recalibrations to provide accurate cutting time predictions. Frequent recalibrations are not feasible in modern dairy plants. Furthermore, the methods disclosed therein require knowledge of the time the enzyme is added to the milk. In a laboratory setting, this is not per se problematic; in industrial application, however, the piping distance between the enzyme supply and the cheese making vat may vary, making the exact determination of the reference time a significant challenge.
More recently, cheese making plants have begun increasing the protein content of the milk by adding dried skim milk solids or removing some of the liquid from milk by ultrafiltration while others have begun decreasing the milk pH (some by using carbon dioxide injection into the milk) to increase the enzymatic reaction rates and produce products with improved functional characteristics. These new and existing challenges have impaired the ability of the previously known methods to provide accurate cutting time predictions over a broader range of protein substrates having different enzymatic reactivities. Accordingly, there is a need in the art for improved devices and methods for accurately predicting the cutting time of a milk coagulum under more variable processing conditions and methods.